Many conventional liquid pumps are directly or indirectly coupled to a switch or similar device that detects a liquid level in order to activate the pump when needed. Activation can include providing a signal to the pump to start or stop operation, and/or providing or removing power to the pump to start or stop the pump from operating. Activation can also include, for example, triggering alarms at pre-determined liquid levels of high and/or low level events.
For many years, a common liquid level control switch consisted of a mercury switch embedded in a foam or plastic “float” housing. The fluctuating liquid level would cause the float to physically move, which would cause the mercury switch to close or open a circuit, depending on whether the mercury switch was normally open or normally closed. Mercury float switches were the industry standard due to their extreme reliability in harsh working environments. However, increasingly stringent regulations regarding products containing mercury have caused the industry to begin a shift toward alternative solutions for the mercury float switch. Currently, the most common alternative is the mechanical float switch.
Although there are several design variations of mechanical float switches on the market, the general perception is that they lack the reliability of the mercury switch design due to a multitude of moving parts inside the float housing. The moving parts can degrade operation by becoming misaligned, damaged due to impact in shipping and/or operation, corrode and cease to operate, become damaged due to electrical arcing and/or chattering, as well as many other failure modes.
Floats with an embedded magnet have also been used to activate or deactivate a switch. Yet, in conventional configurations, the magnet is not adequately secured so as to avoid physical interaction with the float housing or other components of the switch. In addition, the float, with the integrated magnet, is typically positioned in the liquid to be sensed. This can lead to problems with residue buildup and/or floating debris, causing the interaction between the magnet and the switch to degrade and eventually fail.